This invention relates to enzymatic processes for converting glucose (dextrose) to glucosone which can be converted to fructose.
Most food grade glucose is provided as an enzymatic hydrolysate of corn starch, i.e., the corn syrup of commerce. Glucose is generally rated at being 60 to 80% as sweet as sucrose and therefore sells at a correspondingly lower price. It has long been known to isomerize glucose to fructose which is even sweeter than sucrose employing an enzyme having glucose isomerase activity, preferably one which has been immobilized upon an inert support such as diethylaminoethyl-cellulose, porous glass or chitin. The isomerization of glucose provides an equilibrium mixture typically containing 42-50% fructose and is referred to as high fructose corn syrup (HFCS).
Recently, it has been proposed to achieve substantially complete conversion of glucose to fructose by first enzymatically converting glucose to glucosone and thereafter chemically reducing the glucosone to fructose. Thus, in accordance with U.S. Pat. No. 4,246,347, the disclosure of which is incorporated by reference herein, at least about ninety-five percent of D-glucose in aqueous solution is enzymatically oxidized to D-glucosone employing an enzyme having glucose-2-oxidase activity, preferably one obtained from Polyporus obtusus or Aspergillus oryzae, while removing or utilizing co-produced hydrogen peroxide, the D-glucosone being thereafter hydrogenated to D-fructose. As is known in the art the glucose-2-oxidase obtained from Polyporus obtusus, the preferred organism up to the present, is employed in the form of a cell-free extract, primarily because only low enzyme activity is obtained when mycelia of this organism are used as the source of the enzyme.
These conversions, D-glucose to D-glucosone and D-glucosone to D-fructose, can be regarded as proceeding in accordance with the following equations: ##STR1## The enzyme can be used as cell-free extract or in immobilized form employing known procedures.